1. Field of the Invention
The present invention relates to a method for localizing the position of a wireless device in an environment comprising a wireless network having at least one access point.
More in particular, the present invention relates to a method for localizing the position of a wireless device in an environment comprising a wireless network having at least one access point, wherein satellite positioning signals, in particular GPS positioning signals, are not available or provide poor coverage.
2. Present State of the Art
Methods and systems are known in the art for localizing the position of a device, whether fixed or mobile, on the basis of information obtainable through a radio frequency reader built in the device itself and a plurality of radio frequency identifiers, or RFID tags, arranged in a fixed and known manner within an environment.
The position of the device can be determined with variable accuracy on the basis of a triangulation of signals coming from the radio frequency identifiers, identified by a univocal serial number, whose exact position must be known a priori.
The position of such radio frequency identifiers must therefore be obtained beforehand by the device through access to a database by means of any type of connection, e.g. by polling an HTTP service.
As an alternative, the data about the identifiers' position may be preloaded into the device through a wired connection or a memory card.
However, such prior art systems suffer from a few drawbacks.
In the first place, polling a database necessarily requires a connection to the network, whether a local or wide area one, which allows access thereto, with resulting problems of network authentication of the device to be localized.
It is also necessary to know or find the URL address at which the information about the position of the radio frequency identifiers is available.
In addition, the traffic generated by the device to be localized competes with the normal traffic exchanged by other systems, e.g. other Wi-Fi devices such as laptops and smartphones.
In the second place, in the case of memory-preloaded data, although the above problems cannot arise, there are drawbacks related to information updating and to the fact that the device must be located in a well-known and not unforeseen environment.
In fact, it must be taken into account that the devices to be localized are often also conceived for emergency situations (for example, a fireman going into a smoke-saturated environment), and it is unthinkable that the data required for localizing the environment where the emergency situation is occurring have been previously stored in the rescuer's personal localization device or can be stored therein when the rescuer enters the environment.
International patent application No. WO 2010/004081 relates to a method and a system for localizing a device inside a large building, in which GPS positioning signals cannot be received. The method provides for detecting a signal, or “beacon”, periodically transmitted in clear by at least one access point receivable by the device, and retrieving position information, contained in said beacon, about the access point. The beacon structure is defined in the IEEE 802.11 standard and later modifications thereof. Alternatively, the MAC (“Media Access Control”) address of the access point can be read in the beacon, which MAC address is then used for reading the geographic position of the associated access point in a database.
However, the system described in the above mentioned international patent application suffers from the drawback that the accuracy of the system essentially depends on the number of beacons receivable by the device. In fact, in order to obtain a highly accurate position of the device, it is necessary to make a signal triangulation or geometrical calculations. For better accuracy, the number of the wireless network access points should be increased: this would require high hardware costs and would constitute a waste of resources. The database access alternative is disadvantageous because it requires a data connection that might not be available or unfeasible in emergency conditions.
A further drawback of the method described in the above mentioned international patent application is that it is not possible to change in a simple and economical way the position of the geographic reference points within the environment, unless access points are uninstalled and reinstalled or additional access points are added to the wireless network.